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Publications (10)13.39 Total impact

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    ABSTRACT: Nd3+ doped CaF2 single crystal scintillator has been investigated. We tried to grow 1%, 5%, 10%, 20%, 30% and 40% Nd3+ doped CaF2 single crystals by the simple melt-solidifying method. Powder X-ray diffraction (XRD) patterns were measured to identify the phase of all the samples. The XRD patterns of all the samples were similar to CaF2. Those samples are compared in terms of their X-ray-excited radioluminescence spectra, transmittance, α-ray-excited decay time and light yield. When the X-ray is used for excitation, luminescence is observed in the VUV region. Transmittance of the crystals is more than 70% at wavelengths longer than about 180 nm. In the decay kinetics, the fast components of the samples are distributed in less than 25 ns time range and the slow components of sample are distributed in more than 90 ns. These decay times became shorter with increasing Nd3+ concentration. They are related to the Nd3+ 5d-4f VUV emission. The light yields of samples are distributed in 5–2500 photon/5.5 MeV α-ray and decrease with increasing Nd3+ concentration.
    Optical Materials 01/2011; · 2.08 Impact Factor
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    ABSTRACT: Because there is an overlap of the 5d-4f emission transition of Tm<sup>3+</sup> and absorption transition of Nd<sup>3+</sup>, an energy transfer between Nd<sup>3+</sup> and Tm<sup>3+</sup> in LaF<sub>3</sub> was supposed to enhance the efficiency of the previously studied Nd:LaF<sub>3</sub> scintillation material. In this study, 0.1% and 1%Tm, Nd, and Tm, Nd codoped LaF<sub>3</sub> single crystals scintillators were developed using micro-pulling down method (μ-PD), and their optical properties in the vacuum ultraviolet (VUV) region were evaluated. Tm<sup>3+</sup> codopant did not show positive contribution to VUV emission, but energy transfer between Nd<sup>3+</sup> and Tm<sup>3+</sup> cannot be excluded, although the photoluminescence spectra point just to a competition for energy between the two ions. Gamma-ray response was also measured using the pulse-height distribution measurement.
    IEEE Transactions on Nuclear Science 07/2010; · 1.22 Impact Factor
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    ABSTRACT: Tm<sup>3+</sup> doped BaF<sub>2</sub> single crystal scintillator has been investigated. Undoped, 0.1, 0.5, and 1% Tm -doped BaF<sub>2</sub> are compared in terms of their decay time, light yield, non-proportionality and energy resolution. The fast component of Tm doped BaF<sub>2</sub> is characterized by a 5 ~ 6 ns decay time and it can be related to the Tm<sup>3+</sup> 5d - 4f VUV emission from 4f<sup>n-1</sup> 5d low-spin state (parity allowed and spin allowed transition). The light yield of Tm doped BaF<sub>2</sub> is lower with respect to the undoped BaF<sub>2</sub> and systematically decreases with increasing Tm concentration. However, 0.1%Tm:BaF<sub>2</sub> showed a better non-proportionality and energy resolution than the undoped sample.
    IEEE Transactions on Nuclear Science 07/2010; · 1.22 Impact Factor
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    ABSTRACT: Transparent K<sub>3</sub>LuF<sub>6</sub> single crystals doped with rare earth ions were successfully grown by the micro-pulling down method (μ-PD). X-ray diffraction measurements showed that the as-grown crystals possess monoclinic structure with P2<sub>1</sub>/n space group. The radio- and photoluminescence spectra of the grown crystals were measured in the vacuum ultraviolet (VUV) and ultraviolet (UV) region. The intrinsic luminescence of K<sub>3</sub>LuF<sub>6</sub> was observed at 163 and 200 nm. Nd-doped crystals displayed, in contrast, emission at 183 nm, due to the Nd<sup>3+</sup> 5d-4f transition, and their radioluminescence intensity increases with increasing Nd concentration. Tm:K<sub>3</sub>LuF<sub>6</sub> showed high emission intensity at 190 nm in the radio- and photoluminescence spectra (λ<sub>exc</sub> = 155 nm). Moreover, the emission intensity of 0.5%Tm:K<sub>3</sub>LuF<sub>6</sub> was higher than that of 5%Tm:K<sub>3</sub>LuF<sub>6</sub>. Concerning Er:K<sub>3</sub>LuF<sub>6</sub>, the emission at 165 nm was detected for the 0.5%Er:K<sub>3</sub>LuF<sub>6</sub>.
    IEEE Transactions on Nuclear Science 07/2010; · 1.22 Impact Factor
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    ABSTRACT: Abstract-In order to detect the breast cancer at the early stage with high efficiency, we intend to develop positron emission mammography (PEM), using Pr:LuAG single crystal as a scintillator of this scanner. PEM has the same mechanism of PET, where two 511 keV annihilation gamma-rays are detected by two gamma cameras at opposite side, and reconstruction of the data shows the position of the cancer with malignancy grades. After cutting and polishing processes for each crystal to a physical dimensions of 2.1 × 2.1 × 15 mm<sup>3</sup>, Pr:LuAG array covered with BaSO<sub>4</sub> reflector was used as a sensor head. The one camera unit consisted of 20 × 64 pixels optically coupled with three H8500-03 multi anode PMTs. Our PEM required four cameras at each side. Finally, eight cameras were installed in both sides of the prototype instrument and the spatial resolution was evaluated using the <sup>18</sup>F in the breast phantom.
    IEEE Transactions on Nuclear Science 07/2010; · 1.22 Impact Factor
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    ABSTRACT: We have investigated effects of Ce concentration on optical and scintillation properties for Ce doped LiYF<sub>4</sub> [Ce:LiYF<sub>4</sub>] single crystals. Li(Y<sub>1-x</sub>,Ce<sub>x</sub>)F<sub>4</sub> single crystals with more than 75 % transparency were grown by micro-pulling-down method in the range of 0 ≤ x ≤ 0.03 and the crystals with x = 0.05, 0.1 had milky parts originated from remained starting materials. Photoluminescence spectra of all Ce:LiYF<sub>4</sub> crystals indicated two emission peaks from Ce<sup>3+</sup> ion which was substituted for Y<sup>3+</sup> ion site. Light yield and decay time of α-ray irradiation for Ce:LiYF<sub>4</sub> crystals were largely affected by Ce concentration and the largest light yield was observed for the crystal with x = 0.02. In contrast, the decay time systematically became faster with an increase of Ce concentration.
    IEEE Transactions on Nuclear Science 07/2010; · 1.22 Impact Factor
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    ABSTRACT: NdF3 single crystal was efficiently grown from the melt by the micro-pulling-down (μ-PD) method. The grown crystal had a single-phase confirmed by XRD and showed a highly symmetric peak by XRC. Then optical properties and α-ray excited scintillation properties in Vacuum Ultraviolet (VUV) wavelength region were investigated. It showed 60–80% transmittance down to 170 nm, and broad luminescence centered at 175 nm. The light yield and decay time of it were also evaluated under 5.5 MeV α-ray excitation (241Am). The light yield was evacuated to be 60 ± 6 [Ph/5.5 MeV-α], and the decay time was also evacuated to be 6.9 ns under 5.5 MeV α-ray excitation.
    Optical Materials 01/2010; 32(9):878-881. · 2.08 Impact Factor
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    ABSTRACT: BaF2 is an intensively studied scintillator for the detection of gamma radiation due to its relatively high stopping power, radiation hardness and extremely fast response. BaF2 possesses the fast cross-luminescence component at 195 and 220 nm with a lifetime of several hundred picoseconds. However, this component coexists with slow one at 310 nm related to the self-trapped exciton (STE). In our present study, we focused on BaF2 host material and introduced the Tm3+ (activator) 5d-4f vacuum ultraviolet (VUV) luminescence center to suppress the STE luminescence. Tm:BaF2 single crystals were successfully grown by the micro-pulling-down (mu-PD) method with up to 10 mol % of Tm. The STE emission intensity decreased with increasing Tm concentration. Tm3+ 5d-4f emission was observed while cross-luminescence was decreased at higher Tm concentrations.
    Japanese Journal of Applied Physics 01/2010; 49. · 1.07 Impact Factor
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    ABSTRACT: Chemically stable and transparent K2NaLuF6 single crystals doped with Tm3+ ions were grown by the micro-pulling down method (μ-PD). X-ray diffraction measurements showed that the as-grown crystals possess cubic structure with Fm3m space group. The radio- and photo-luminescence spectra of the grown crystals were measured in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions. Tm:K2NaLuF6 showed high emission intensity at 188 nm in the radio- and photo-luminescence spectra (λexc = 159 nm). The decay time and light yield of Tm:K2NaLuF6 were also investigated by 241Am 5.5 MeV α-ray irradiation. The main component of the decay time was a 4–8 μs and this emission was considered as 5d–4f emission from 4fn − 15d high-spin state (parity allowed and spin forbidden transition). In addition to this, the light yield of Tm-doped K2NaLuF6 single crystals systematically increased with increasing Tm concentration.
    Optical Materials 01/2010; · 2.08 Impact Factor
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    ABSTRACT: Nd3+ doped CaF2 single crystal scintillator has been investigated. We tried to grow 1, 5, 10, 20, 30 and 40% Nd doped CaF2 single crystals by the simple melt-solidifying method. Those sampeles are compared in terms of their X-ray excited radio luminescence spectra, transmittance, ¿-ray radiated decay time and light yield. When they are irradiated by X-ray the luminescence appears at VUV region. Transmittances of them are more than 70% at wavelengths longer than about 180 nm. In decay time kinetics, the fast components of Nd doped CaF2 are distributed in 8-40 nsec and became shorter with increasing of concentration of Nd. they are related to the Nd3+ 5d-4f VUV emission. The light yield of Nd doped CaF2 are distributed in 5-2500 photon/5.5MeV ¿ and decrease with the increasing of the amount of Nd concentrations.
    IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium 01/2009;